Abstract Background: Chronic non-cancer pain and substance use disorders frequently co-occur in VA primary care and addictions treatment settings. The treatment for pain is complicated in veterans with a history of alcohol or drug misuse because of a potential for abuse and diversion of many prescription pain medications. Thus, treatment providers are left without successful and empirically-supported methods for treating the large number of patients with chronic pain who also have past or current substance use disorders. One potential strategy is to use cognitive-behavioral treatment (CBT) interventions to manage pain and decrease substance use abuse/misuse. Psychosocial interventionssuch as CBT have demonstrated efficacy for reducing pain and improving functioning in persons with a broad spectrum of pain-related problems. However, this form of treatment has not been explicitly tested in patients with co-occurring substance use disorders. Determining the effectiveness of a psychosocial intervention targeting both pain and substance use disorders would greatly increase the available treatment options for veterans with these conditions. Project Objectives: This project is designed to test the effect of a CBT intervention for patients with chronic pain who are already engaged in VA treatment for substance use disorders compared to treatment as usual on measures of pain intensity, pain-related disability and pain-tolerance. A set of secondary analyses will examine if group CBT compared to the treatment as usual condition is associated with greater reductions in illicit substance use over the follow-up time period and whether during-treatment reductions in pain mediate the effect of treatment assignment on later substance use. Finally, a series of secondary analyses will explore whether the hypothesized mechanisms of action for the CBT intervention mediate the effect of this intervention on pain intensity and pain tolerance. Methods: The proposed study is a randomized controlled trial of group-based CBT compared to treatment as usual in patients currently receiving drug and alcohol treatment. A total of 128 Veterans with alcohol or drug abuse or dependence and at least moderate pain currently treated in the Ann Arbor VA Substance Use Disorder treatment clinic will be assessed at baseline and then randomly assigned to one of these two conditions. These patients will be re-assessed at 3-months (i.e. immediately post treatment), 6-months and 12- months. The primary outcomes will be pain intensity, pain-related disability and pain tolerance. Mixed model regression analyses will be used for all primary analyses to estimate between-group differences in changes in individual slopes over time. Finally, a series of secondary analyses will explore (a) whether the intervention influences post-treatment substance use, (b) if change in pain during treatment mediates the effect of the intervention on subsequent substance use and (c) whether the hypothesized mechanisms of action for the CBT intervention mediate the effect of this intervention on pain intensity and pain tolerance.